A method and an arrangement for controlling the power of an internal combustion engine are disclosed in British Patent 1,603,921. In this patent, a throttle flap in the intake system of the internal combustion engine is adjusted in the context of a position control circuit in order to control the power of the engine in dependence upon the driver command. The rate of change of the throttle flap is limited in dependence upon the rpm of the engine in order to adapt the time response of the displacement of the accelerator pedal and of the throttle flap to the dynamic conditions of the mixture formation of the mixture and of the mixture transport. With this measure, a reduced emission of toxic substances occurs in the transient range.
The optimal rate of conversion of a catalytic converter lies in a very narrow window of the air/fuel ratio. For steady state or quasi steady state operating states of the engine, the exhaust-gas control ensures that this window is maintained as exact as possible. If the driver suddenly depresses the accelerator pedal, then the air quantity or air mass supplied to the engine increases rapidly. If the increase of the air quantity or air mass drops in a time interval wherein the metering of fuel for a cylinder has already taken place, but the intake operation has not ended, then this causes the condition that the cylinder is supplied with a mixture which is too lean. If the mixture is still capable of being ignited, then the nitrogen oxide emissions thereby increase. If the mixture is no longer capable of being ignited, then the hydrocarbon emissions increase.
Furthermore, a so-called gap in acceleration occurs which is a situation wherein the motor vehicle no longer accelerates directly with the actuation with the accelerator pedal and the engine rpm no longer increases directly with the actuation of the accelerator pedal. If the driver suddenly lets go of the accelerator pedal, then the situation can occur that a cylinder, for which fuel has already been injected, is supplied with a quantity of air which is too little in comparison to the quantity of fuel already injected. This results in a mixture which is too rich and which has increased carbon monoxide and hydrocarbon emissions.
Furthermore, it is difficult to exactly compute the quantity of air supplied to the individual cylinders when there are rapid changes of the throttle flap because of the impreciseness in the transport of the fuel mixture to the cylinder. In this way, the computation of the required fuel quantity exhibits a certain inaccuracy. This inaccuracy cannot the compensated by the exhaust-gas control because of its time constants. An improvement in this regard is obtained by the electric control of the throttle flap in dependence upon the driver command when the driver command is filtered in such a manner that a sudden depression of the accelerator pedal is transmitted to the throttle flap only after being smoothed. With this measure, the rate of change of the air quantity supplied to the cylinders is limited. In this way, the mismatch between air and fuel quantities can be reduced.
In the state of the art, the speed of changing the throttle flap is generally limited in dependence upon the engine rpm. Such a limitation of the throttle flap displacement speed operates independently of the operating states in which the above-mentioned mismatch occurs more often. Such operating conditions are especially the warm-up of the engine and when the ambient air is colder. Accordingly, the disadvantage of the rpm dependent limitation is that the motor vehicle only reacts with delay to a depression of the accelerator pedal independently of the problematic of the exhaust gas and therefore driving performance is reduced.